The overall objective of the proposal is to develop and evaluate a photon counting and energy resolving breast computed tomography system. In every medical imaging modality, the aim is to generate the best image at the lowest dose possible. The tradeoff between image quality and patient dose is always an important consideration in designing a medical imaging system. In this study, we propose a breast CT system that has the capability of producing images of higher quality at a reduced dose compared to current breast CT systems. The key to the system involves a photon counting and energy resolving x-ray detector that is made of CdZnTe (CZT) crystals. Intrinsically, CZT has excellent energy absorption efficiency due to its large effective atomic number (49.6) and high mass density (5.8 g/cm3)-allowing for great radiation stopping power. Photon counting detectors allow for the recording of each x-ray photon and its energy as it is absorbed by the CZT. When a photon strikes the detector, electrons and holes are created and a current is produced by the propagation of electrons and holes. The amount of current produced is directly proportional to the energy of the photon. A threshold determines the current level at which a photon is counted. By setting an appropriate threshold, electronic and Swank noise can be completely rejected. Properties of low noise and high quantum efficiency translate to higher image signal-to-noise ratio (SNR) at a lower dose. The SNR of breast CT systems utilizing a photon counting detector can be improved by 30% as compared to those with a charge-integrating flat panel detector. An SNR improvement of 30% equals a dose reduction of 40% percent in breast CT. Our proposed CT system is expected to realize at least the same amount of dose reduction while improving cancer detection sensitivity by exploiting its energy resolving capability. The specific aims of this proposal are: 1) Construct a photon counting, slit-scanning breast computed tomography system using CZT detector for phantom and post-mortem studies, 2) Investigate the hypothesis that a CZT photon-counting CT system produces images of higher quality at a reduced dose, and 3) Evaluate the benefits afforded by the energy resolving capability of the detector. PUBLIC HEALTH RELEVANCE: Breast cancer is the fifth most common cause of cancer death-for women it is the leading cause of all cancer death, responsible for over half a million deaths worldwide. The sensitivity of mammography in detecting cancer is estimated to be 75-85%, and for dense breasts it is significantly lower. A photon-counting breast CT system has the potential to provide clinicians with images of high quality at a low dose, and therefore improve cancer detectability.